Water heating and storage system

ABSTRACT

A dual mode operative water heating and storage system including a hot water storage tank having a cold water supply inlet for replenishing water withdrawn from the tank, a conduit system for normally circulating water from a lower to an upper level of the tank and including means for heating the circulated water, means connected into the system for withdrawing heated water up to a given rate of flow which is in excess of the rate at which water is normally circulated through the conduit system, and means for connecting the upper level of the tank in flow communication with the withdrawal means whenever the withdrawal rate exceeds the normal circulation rate.

United States Patent Kirschner 1 Sept. 5, 1972 [54] WATER HEATING ANDSTORAGE SYSTEM [72] Inventors: Robert F. Kirschner, Lakeville,

Mass.

[22] Filed: Nov. 27, 1970 [21] Appl. No.: 93,342

[52] US. Cl. ..165/l08, 122/33, 126/362, 219/316,165/132 [51] Int. Cl..F24h 01/18 [58] Field of Search ..l65/132, 108; 126/362; 219/316;122/33 [56] References Cited UNITED STATES PATENTS 1,890,263 12/1932Parent "126/362 X 3,447,560 6/ 1969 Dodson et al ..126/362 X HOT WA TEEOUTLE7 22 Q 367 40 l/WMP C UNTROL POI/V7 Stranko ..l65/108 Morgan et al..165/l08 X Primary Examiner-Albert W. Davis, Jr. Attorney-Bean & Bean[57] ABSTRACT A dual mode operative water heating and storage systemincluding a hot water storage tank having a cold water supply inlet forreplenishing water withdrawn from the tank, a conduit system fornormally circulating water from a lower to an upper level of the tankand including means for heating the circulated water, means connectedinto the system for withdrawing heated water up to a given rate of flowwhich is in excess of the rate at which water is normally circulatedthrough the conduit system, and means for connecting the upper level ofthe tank in flow communication with the withdrawal means whenever thewithdrawal rate exceeds the normal circulation rate.

27 Claims, 3 Drawing Figures DEF COL 11 WATER J PATENTEDSEP 5 I972 SHEET2 0F 2 luN QUkQ? QJOU INVENTOR ROBERT F. KIRSCHN ER WATER HEATING ANDSTORAGE SYSTEM SUMMARY OF THE INVENTION The present invention relates toa water heating and storage system which is particularly adapted by wayof example for use in a multiple dwelling or office building waterheating facility or the like, and overcomes certain deficiencies ofprevious systems.

The invention features provision of a single water heating and storagetank having a cold water supply inlet for replenishing water withdrawnfrom the tank; and a shrouded heat exchanger, which receives water to beheated at its inner end portion from a novel selective flow source/ratefeed conduit system and is connected into a hot water delivery conduitat its outer end portion. The conduit system includes a first conduitleading from a lower intake manifold for drawing in water fromsubstantially throughout the lower level of the tank, and a secondconduit leading from a combination intake/outlet upper manifoldextending horizontally throughout a substantial portion of the upperlevel of the tank. In one preferred form of conduit system arrangementthe upper manifold extends outwardly of the tank for flow communicationwith the outlet end portion of the shrouded heat exchanger and includesa continuously running pump normally inducing a constant circulation ofwater from the lower level of the tank, through the heater, and backinto the upper level of the tank.

The first conduit is designed so as to permit only a normal rate of flowof water from the lower levels of the tank into the heater, equivalentto the rate of circulation through the pump plus withdrawals from thesystem at normal rates; in accordance with the designed heat exchangerecovery rate of the system. A pre-selected flow rate restrictingorifice installed in the line of the first conduit provides a practicaland convenient method for establishing this first conduit flow rateparameter. The second conduit includes an inline valve device, which isoperable to selectively connect the upper manifold in flow communicationwith the heater only whenever the rate of withdrawal of water throughthe delivery conduit exceeds the permitted rate of flow of water throughthe flow limiting orifice of the first conduit, as explainedhereinabove.

Thus, during normal circulation operation and/or during normalwithdrawals of hot water from the system, heater intake water is drawnsolely from the lower level of the tank through the lower manifold; anyheated water withdrawn from the system being replaced by cold supplywater entering into the lower level of the tank. However, when hot waterwithdrawal demands are in excess of the flow rate determined by the flowlimiting orifice, the valve in the second conduit automatically opens topermit previously heated water to be withdrawn from the upper level ofthe tank through the upper manifold and into the delivery conduitsystem, at a rate sufficient to satisfy the excess demand.

The system is therefore automatically balanced with respect to storagewater heating and hot water delivery requirements, and insures deliveryof water at a prescribed temperature, while at the same time maintaininghighly desirable temperature Stratification conditions interiorly of thetank. By positively promoting stratification conditions within the tank,a smaller tank than conventionally required may be used for any givenapplication.

The present system also provides for a more even and precise control oftemperature, and therefore permits a more even draw of energy from theheat source.

DRAWINGS The nature and mode of operation of the present invention willnow be more fully described in the following detailed description takenwith the accompanying drawings wherein:

FIG. 1 of the drawing herewith comprises a. schematic illustration ofone form of the water heating and storage system of the presentinvention;

' FIG. 2 is a drawing corresponding to FIG. 1, butillustrating amodified form of the present invention; and

FIG. 3 is a fragmentary view illustrating analternative construction,which may be employed in either of the systems shown in FIGS. 1 and 2.

DETAILED DESCRIPTION As illustrated in FIG. 1 of the drawing herewith,the invention may be embodied in a heated'water delivery systemincluding a storage tank 10 having a cold water inlet connection 12 forreplenishing hot water withdrawn from the tank. A heater unit,designated generally at 14 includes a tubular shaped shroud 16 housing abundle of return bent heat-exchange tubes 18, which extend from a tubesheet and steam supply assembly 20 closing the outer end of the shroud16. Altemately disposed baffle plates 21 are preferably ar ranged withinshroud 16 to guide the flow of water therethrough along an undulation orzig-zag path relative to tubes 18 to insure maximum heat exchangeefficiency. A heated water delivery conduit 22 is arranged incommunication with the interior of the shroud 16 adjacent its deliveryend portion, which as shown in the drawing, may be preferably bearranged exteriorly of tank 10. I

The inlet end portion of shroud 16 is disposed interiorly of tank 10 andis connected in open communica tion by means of a conduit-fitting 24with first and second feed conduits 26 and 28, respectively. The firstor lower conduit 26 communicates with the interior of tank 10 by way ofexample through a lower intake manifold 30, which extends horizontallythroughout a substantial portion of the lower level of the tank.Manifold 30"may conveniently be constructed as a tubular conduitperforated at intervals therealong, as indicated at 32, to permit thewithdrawal of water from the lower level of the tank in gentle andevenly distributed manner. This construction avoids excessiveturbulences and agitations of the stratified cold water within the lowerlevels of the tank, such as normally occur during draw and heat recoveryperiods. Also, a deflector 34 is preferably provided to guide the coldwater supply entering the tank through inlet connection 12 so as totravel downwardly and across the bottom surface of the tank, therebyfurther avoiding a breakdown of the natural temperature stratificationmechanism operating within the tank.

A conduit 36 is provided to extend from heated water withdrawal conduit22 to the intake of a continuously running pump 40 and from thedischarge of the pump into an upper manifold or sparger" 42, whichextends horizontally throughout a substantial portion of the upper levelof the tank. Manifold 42 is perforated at intervals therealong, asindicated at 43, in order to permit the gentle and even introduction ofheated water into, or withdrawal of heated water from, the upper levelof tank 10, and is arranged to be normally excommunicated from but onoccasion in flow communication with said second conduit 28 through meansof a valve device 44, which is selectively operable between closed andvariably open positions.

Thus, pump 40 normally operates to draw water from across substantiallythe entire lower level of tank 10, through the manifold 30; firstconduit 26; heater unit 14; conduit 22; and to then discharge it throughupper manifold 42 across substantially the entire upper level of thetank. By nature, the less dense heated water floats on top of therelatively cold supply water introduced into the lower level of tank inthe absence of external turbulating influences.

Valve 44 is a pressure-differential responsive type valve and isadjusted so as to remain closed when operating under pressuredifferentials such as are encountered only under normal operations ofthe system; as induced by operation of the circulating pump 40 andnormal withdrawals of heated water within the range of the recovery ratedesign of the system. Thus, under idling (no withdrawal and/or normal"withdrawal) conditions, pump 40 operates to gently circulate water fromthe lower level of the tank, through the heater, and then into the upperlevel of the tank; thereby maintaining and/or gradually bringing theentire tank contents at or to the desired temperature, withoutdisturbing in the meantime the natural temperature Stratificationphenomenon within the tank.

However, should withdrawals of hot water through conduit 22 increasesubstantially above the pump circulation rate, the hot water flowcontrol valve 44 will open so as to allow appropriate amounts of hotwater to be drawn from the upper level of the tank in through manifold42 and to be mixed with water being drawn in through manifold 30; andthen to be passed through the heater unit 14 into delivery conduit 22.Thus, the withdrawal of hot water from the upper level of the tank tomeet the excess demand imposes no appreciable additional load on theheat energy supply system, yet insures that water delivered by conduit22 to the point of intended use under such condition is at theprescribed temperature.

As explained hereinabove, it is a particular feature of the presentinvention that the conduit 26 is restricted to convey water at only aprescribed rate, such as by provision of the orifice device asillustrated at 46, which is of a properly pre-selected dimension.Orifice device 46 may be of any suitable design, and for example maysimply comprise an apertured disc engaged between opposite face plates,which are threaded onto opposite ends of tubings comprising conduit 26.In any case, the How aperture of orifice device 46 is sized so as topermit a rate of flow substantially equal to the heat exchange recoveryrate of the system before developing a pressure drop across the orifice(at the pump circulation rate) such as will operate to cause the valve44 to open. While the rate of flow 'of relatively cold water from thelower level of tank 10 may be limited by merely reducing the diameter ofeither or both of manifold 30 and first conduit 26, the utilization ofdevice 46 is preferred, since it facilitates initial design andinstallation and permits the system to be readily adjusted to meetvarying requirements of any given installation.

Hence, it will be appreciated that during idling and/or normalwithdrawal conditions, orifice 46 is operative to permit the requisiterate of flow from the lower level of tank 10, and the valve 44 is thenoperative to prevent any undesirable short-circuiting of hot water flowfrom within the upper manifold 42 through conduit 28 and back throughthe heater unit. However, whenever withdrawals of heated water in excessof the recovery rate of the system are being made, the orifice device 46induces a differential pressure condition to exist between conduits26-28 and the interior of tank 10, thereby causing valve 44 to open andpermit delivery of an additional supply of previously heated water fromthe upper level of the tank to flow into and through the upper manifoldand the heater unit, and thence out through the delivery conduit.

Particularly in cases where pump 40 is not of the positive displacementvariety, it is preferable to provide a flow check valve 52in the line ofthe pump discharge, to prevent any back-flow of water from the upperlevel of the tank in reverse direction through the pump and into thewater delivery conduit when heated water withdrawals are being made;thus insuring that all water entering the withdrawal system will be upto the prescribed temperature.

A temperature sensor 55, which is preferably positioned adjacent theoutlet end portion of the heater shroud 16, will at all times accuratelynote the temperature of water passing from the heater unit and willserve to properly control the heat energy supply to the heater unit, asis well known in the art. Should the entire contents of the tank attainthe prescribed temperature, the sensor will deenergize the heater untilsuch time as the temperature of the circulating water falls below thedesired withdrawal temperature.

The valve 44 may be of any acceptable design. For example, it may be ofthe spring-loaded pressurebalance type, operating strictly in responseto pressure differentials when the system is out of fluid flow balance,"due to any excessive hot water withdrawal demands. Or, alternatively,the control valve may be of the air pressure actuated type;operationally functional in proportion to readings from a pressuredifferential sensor and actuator measuring the pressure drop across theorifice device 46 or the withdrawal flow rate within conduit 22.

FIG. 2 illustrates a modified form of the heating system of the presentinvention, wherein similar components are designated by similar primenumerals. Whereas in this form, the heater-storage tank 10 isillustrated as being of the upright type, it is to be understood thatthe tank may with equal facility be provided in the form of ahorizontally disposed tank. In FIG. 2, lower manifold 30', uppermanifold 42' and conduit-fitting device 24' are shown as being extendedthrough one side wall of tank 10', so as to position the first andsecond conduits 26' and 28' exteriorly of the tank in order tofacilitate adjustment and/or main tenance of flow control valve 44' andorifice device 46'.

Further FIG. 2 illustrates an arrangement whereby the heating elements18 may be withdrawn from shroud 16 without loss of water from tank andwithout interruption of the facility for withdrawal of hot water throughdelivery conduit 22' from the upper level of the tank. To this end, aby-pass conduit 95 hav ing a normally closed valve 96 is arranged todirectly connect conduit 22' into the top of tank 10', and normally openvalves 99 and 100 are provided in conduit 22' adjacent the outlet endportion of shroud l6 and in conduit-fitting 24', respectively. Thus,when valves 99 and 100 are closed and valve 96 is open, the interior ofshroud 16' is functionally isolated from the rest of the heating system,and conduit 22' is connected in direct flow communication with the top,of tank 10. Further, it is preferable to provide normally open valves 97and 98 in line 36' at positions upstream and downstream of pump 40' inorder to permit maintenance on or replacement of pump 40'.

FIG. 3 illustrates another alternative construction, wherein the coldwater supply inlet 12" of tank 10" is connected directly into lowermanifold 30". This arrangement may in some cases be desirable from thestandpoint that it both simplifies the tank construction and preventsundesirable turbulent water flow patterns within the tank upon admissionof cold supply water during a heated water draw period.

Thus, it will be appreciated that the invention provides a novel dualmode operative water heating and storage and delivery system embodyingvarious important features and advantages as set forth hereinabove.While the invention has been illustrated and described with referenceonly to a heating system employing a steam energized type immersionheater, it will be understood that any other form of heater and heatenergy source may be employed.

We claim:

1. A water heating and storage system comprising in combination:

a hot water storage tank;

means, including means for heating water passing therethrough, fornormally circulating water from a lower region of the tank to an upperregion of the tank, thereby tending to establish a reservoir ofrelatively hot water at least in the upper region of the tank;

first intake means disposed within the lower region of the tank andconnected to the circulation means upstream of the heater means forpermitting inflow of water to the circulation means from the lowerregion at up to a predetermined flow rate;

second intake means disposed within the upper region of the tank andconnected to the circulation means upstream of the heater means;

outlet means connected to the circulation meansdownstream of the heatermeans for delivering heated water to a point of use at up to a flow rategreater than the predetermined flow rate capacity of the first intakemeans;

inlet means for supplying relatively cold water to the lower region ofthe tank to replenish water withdrawn from the tank through the outletmeans; and

normally closed valve means associated with the second intake means foradmitting water to the circulation means from the upper region of thetank when the flow rate demand on the outlet means exceeds thepredetermined flow rate capacity of the first intake means.

2. A water heating and storage system according to claim 1, wherein thepredetermined flow rate capacity of the first intake means is notsubstantially greater than the rate at which water is normallycirculated by said circulation means.

3. A water heating and storage system according to claim 1, wherein thefirst intake means includes flow restricting orifice means for limitingthe rate of flow of water passing to the circulation means from thelower region of the tank.

4. A water heating and storage system according to claim 1, wherein thepredetermined flow rate capacity of the first intake means is notsubstantially greater than the heat exchange recovery rate of the heatermeans.

5. A water heating and storage system according to claim 1, wherein thefirst intake means is directly connected to the cold water inlet means.

6. A water heating and storage system according to claim 1, wherein thevalve means comprises a pressureresponsive valve that opens in responseto the pressure differential created thereacross when the flow ratedemand on the outlet means exceeds the predetermined flow rate capacityof the first intake means.

7. A water heating and storage system according to claim 1, wherein:

the first intake means includes a first manifold extending generallyhorizontally within the lower region of the tank; and

the second intake means includes a second manifold extending generallyhorizontally within the upper region of the tank.

8. A water heating and storage system according to claim 7, wherein thesecond manifold is connected to the circulation means downstream of theof the heater means for delivering heated water to the upper region ofthe tank.

9. A water heating and storage system according to claim 7 wherein:

the first intake means further comprises flow restricting orifice meansinterposed between the first manifold and the circulation means forlimiting the rate of inflow of water through the first manifold; and thevalve means comprises a pressure-responsive valve interposed between thesecond manifold and the circulation means.

10. A water heating and storage system according to claim 9 wherein theflow rate capacity of the first intake means is limited by the flowrestricting orifice means to substantially equal to or less than theheat exchange recovery rate of the heater means.

11. A water heating and storage system according to claim 1, wherein thepredetermined flow rate capacity of the first intake means issubstantially equal to the heat exchange recovery rate of the heatermeans.

12. A water heating and storage system including in combination;

tank means having cold water supply inlet means for replenishing waterwithdrawn from said tank means;

a shroud having an inlet end portion extending inwardly of said tank andhaving an outlet end portion arranged exteriorly of said tank;

immersion heater means arranged within said shroud for heating waterpassing therethrough;

hot water withdrawal means connected into said outlet end portion forwithdrawing heated water from said tank at up to a given rate of flow;

first water intake means disposed within a lower region of said tankmeans and connected in flow communication with said inlet end portionfor permitting inflow of water to said inlet end portion to up to a rateless than said given rate of flow, thereby to insure that water passingfrom said lower region is heated up to a desired withdrawal temperatureby said heater means;

hot water conduit means connecting said outlet end portion in fiowcommunication with an upper region of said tank and including pump meansfor normally circulating water between said tank regions successivelythrough said first water intake means, said shroud and said hot waterconduit means, thereby tending to establish a reservoir of water at ornear said desired withdrawal temperature in at least said upper regionof said tank means;

second water intake means disposed within said upper region of said tankmeans and connected in flow communication with said inlet end portion;and

normally closed valve means associated with said second water intakemeans for admitting water therethrough to said inlet end portion fromsaid upper region whenever the rate of flow of water withdrawn throughsaid hot water withdrawal means is greater than the flow rate capacityof said first water intake means.

13. A water heating and storage system according to claim 12, whereinsaid cold water supply inlet means is connected into said first waterintake means.

14. A water heating and storage system according to claim 12, whereinthe maximum flow rate capacity of said first water intake means is notsubstantially greater than the heat exchange recovery rate of saidheater means.

15. A water heating and storage system according to claim 12, whereinsaid first water intake means includes separate flow restriction meansfor limiting the rate of flow of water therethrough.

16. A water heating and storage system according to claim 15, whereinsaid flow restriction means is an orifice defining plate.

17. A water heating and storage system according to claim 12, wherein:

said first water intake means includes an apertured lower manifoldextending substantially horizontally within said lower region of saidtank means and a vertically extending first conduit connecting saidlower manifold to said inlet end portion;

said hot water conduit means includes an apertured upper manifoldextending substantially horizontally within said upper region of saidtank means;

said second intake means includes a vertically extending second conduitconnecting said upper manifold to said inlet end portion; and

said valve means are arranged in said second conduit, whereby said valvemeans admits water from said upper region through said upper manifoldand said first conduit to said inlet end portion whenever water iswithdrawn from said hot water withdrawal means at a rate greater thanthe maximum flow rate capacity of said first intake means. 18. A waterheating and storage system according to claim 17, wherein said firstwater intake means includes flow restriction means arranged in saidfirst conduit.

19. A water heating and storage system according to claim 18, whereinsaid first and second conduits are arranged to extend exteriorly of saidtank means to facilitate access to said valve means and said flowrestriction means.

20. A water heating storage system according to claim 12 furthercomprising:

by-pass conduit means, including second normally closed valve meansarranged exteriorly of said tank means, connecting said hot waterwithdrawal means to said upper region of said tank means;

normally open valve means arranged exteriorly of said tank means forcontrolling flow of water from said outlet end portion to said hot waterwithdrawal means; and

normally open valve means arranged exteriorly of said tank means forcontrolling flow of water from said first water intake means to saidinlet end portion, whereby when said normally open valve means areclosed and said second normally closed valve means is opened, saidimmersion heater may be withdrawn from said shroud without loss of waterfrom said tank means and hot water may be withdrawn through said hotwater withdrawal means directly from said upper region of said tankmeans.

21. A water heating and storage system according to claim 20, whereinnormally open valve means are arranged exteriorly of said tank means insaid hot water conduit means upstream and downstream of said pump means,such that when the last said valve means are closed said pump means maybe removed without loss of water from said tank means.

22. A water heating and storage system according to claim 12, whereinsaid hot water conduit means includes a conduit extending into saidupper region of.

ceeds the maximum flow rate capacity of said first water intake means.

25. A water heating and storage system comprising in combination:

a hot water storage tank including a relatively cold water supply inletfor replenishing water withdrawn from said tank;

outlet means for withdrawing heated water from said tank at up to agiven rate of flow;

a conduit system for normally circulating water from a lower to an upperregion in said tank, said conduit system having heating means forheating water being circulated therethrough, thereby tending to bringthe contents of said tank at least at said upper region up topredetermined withdrawal temperature, said outlet means being connectedinflow communication with said conduit system downstream of said heatermeans;

first and second tank water intake means in said conduit system upstreamof said heater means, said first intake means being disposed in saidlower region for supplying water to said heater means at up to an amountbelow said given rate of flow, and said second intake means beingdisposed in said upper region for supplying a flow of water from saidupper region to said heater means whenever the rate at which heatedwater is withdrawn through said outlet means exceeds said amount at arate accommodating for the difference between said withdrawal rate andsaid amount.

26. A water heating and storage system according to claim 25, whereinsaid first intake means produces a predetermined pressure differentialin said conduit system upstream of said heater means relative to saidtank whenever said first intake means tends to take in water exceedingsaid amount due to the hot water withdrawal demand on said outlet meansexceeding said amount, and said second intake means includes valve meansoperable by said pressure differential.

27. A water heating and storage system according to claim 1, wherein thecirculation means includes a conduit extending into the upper region ofthe tank for delivering heated water thereto, and the second intakemeans is in part comprised by said conduit.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,688,839Dated September '5. 1972 Inventor(s) Robert F. Kirschner' It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 7, lines 2, 3, 8 and 19, "said tank" should read -said tankmeans",-

Column 8, line 1, are" should read --is-.

Signed and sealed this 13th day of Marohl973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. v ROBERT GOTTSCHALK Commissioner of PatentsAttesting Officer zgx g UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent NO- 3,688,839 Dated September 5. 1972 Inventor(s)Robert F. Kirschner It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 7, lines 2, 3, 8 and 19, "said tank" should read --said tankmeans--,'

Column line 1, are" should read --is--.

Signed and sealed this 13th day of March 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. 7 ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents

1. A water heating and storage system comprising in combination: a hotwater storage tank; means, including means for heating water passingtherethrough, for normally circulating water from a lower region of thetank to an upper region of the tank, thereby tending to establish areservoir of relatively hot water at least in the upper region of thetank; first intake means disposed within the lower region of the tankand connected to the circulation means upstream of the heater means forpermitting inflow of water to the circulation means from the lowerregion at up to a predetermined flow rate; second intake means disposedwithin the upper region of the tank and connected to the circulationmeans upstream of the heater means; outlet means connected to thecirculation means downstream of the heater means for delivering heatedwater to a point of use at up to a flow rate greater than thepredetermined flow rate capacity of the first intake means; inlet meansfor supplying relatively cold water to the lower region of the tank toreplenish water withdrawn from the tank through the outlet means; andnormally closed valve means associated with the second intake means foradmitting water to the circulation means from the upper region of thetank when the flow rate demand on the outlet means exceeds thepredetermined flow rate capacity of the first intake means.
 2. A waterheating and storage system according to claim 1, wherein thepredetermined flow rate capacity of the first intake means is notsubstantially greater than the rate at which water is normallycirculated by said circulation means.
 3. A water heating and storagesystem according to claim 1, wherein the first intake means includesflow restricting orifice means for limiting the rate of flow of waterpassing to the circulation means from the lower region of the tank.
 4. Awater heating and storage system according to claim 1, wherein thepredetermined flow rate capacity of the first intake means is notsubstantially greater than the heat exchange recovery rate of the heatermeans.
 5. A water heating and storage system according to claim 1,wherein the first intake means is directly connected to the cold waterinlet means.
 6. A water heating and storage system according to claim 1,wherein the valve means comprises a pressure-responsive valve that opensin response to the pressure differential created thereacross when theflow rate demand on the outlet means exceeds the predetermined flow ratecapacity of the first intake means.
 7. A water heating and storagesystem according to claim 1, wherein: the first intake means includes afirst manifold extending generally horizontally within the lower regionof the tank; and the second intake means includes a second manifoldextending generally horizontally within the upper region of the tank. 8.A water heating and storage system according to claim 7, wherein thesecond manifold is connected to the circulation means downstream of theof the heater means for delivering heated water to the upper region ofthe tank.
 9. A water heating and storage system according to claim 7wherein: the first intake means further comprises flow restrictingorifice means interposed between the first manifold and the circulationmeans for limiting the rate of inflow of water through the firstmanifold; and the valve means comprises a pressure-responsive valveinterposed between the second manifold and the circulation means.
 10. Awater heating and storage system according to claim 9 wherein the flowrate capacity of the first intake means is limited by the flowrestricting orifice means to substantially equal to or less than theheat exchange recovery rate of the heater means.
 11. A water heating andstorage system according to claim 1, wherein the predetermined flow ratecapacity of the first intake means is substantially equal to the heatexchange recovery rate of the heater means.
 12. A water heating andstorage system including in combination; tank means having cold watersupply inlet means for replenishing water withdrawn from said tankmeans; a shroud having an inlet end portion extending inwardly of saidtank and having an outlet end portion arranged exteriorly of said tank;immersion heater means arranged within said shroud for heating waterpassing therethrough; hot water withdrawal means connected into saidoutlet end portion for withdrawing heated water from said tank at up toa given rate of flow; first water intake means disposed within a lowerregion of said tank means and connected in flow communication with saidinlet end portion for permitting inflow of water to said inlet endportion to up to a rate less than said given rate of flow, thereby toinsure that water passing from said lower region is heated up to adesired withdrawal temperature by said heater means; hot water conduitmeans connecting said outlet end portion in flow communication with anupper region of said tank and including pump means for normallycirculating water between said tank regions successively through saidfirst water intake means, said shroud and said hot water conduit means,thereby tending to establish a reservoir of water at or near saiddesired withdrawal temperature in at least said upper region of saidtank means; second water intake means disposed within said upper regionof said tank means and connected in flow communication with said inletend portion; and normally closed valve means associated with said secondwater intake means for admitting water therethrough to said inlet endportion from said upper region whenever the rate of flow of waterwithdrawn through said hot water withdrawal means is greater than theflow rate capacity of said first water intake means.
 13. A water heatingand storage system according to claim 12, wherein said cold water supplyinlet means is connected into said first water intake means.
 14. A waterheating and storage system according to claim 12, wherein the maximumflow rate capacity of said first water intake means is not substantiallygreater than the heat exchange recovery rate of said heater means.
 15. Awater heating and storage system according to claim 12, wherein saidfirst water intake means includes separate flow restriction means forlimiting the rate of flow of water therethrough.
 16. A water heating andstorage system according to claim 15, wherein said flow restrictionmeans is an orifice defining plate.
 17. A water heating and storagesystem according to claim 12, wherein: said first water intake meansincludes an apertured lower manifold extending substantiallyhorizontally within said lower region of said tank means and avertically extending first conduit connecting said lower manifold tosaid inlet end portion; said hot water conduit means includes anapertured upper manifold extending substantially horizontally withinsaid upper region of said tank means; said second intake means includesa vertically extending second conduit connecting said upper manifold tosaid inlet end portion; and said valve means are arranged in said secondconduit, whereby said valve means admits water from said upper regionthrough said upper manifold and said first conduit to said inlet endportion whenever water is withdrawn from said hot water withdrawal meansat a rate greater than the Maximum flow rate capacity of said firstintake means.
 18. A water heating and storage system according to claim17, wherein said first water intake means includes flow restrictionmeans arranged in said first conduit.
 19. A water heating and storagesystem according to claim 18, wherein said first and second conduits arearranged to extend exteriorly of said tank means to facilitate access tosaid valve means and said flow restriction means.
 20. A water heatingstorage system according to claim 12 further comprising: by-pass conduitmeans, including second normally closed valve means arranged exteriorlyof said tank means, connecting said hot water withdrawal means to saidupper region of said tank means; normally open valve means arrangedexteriorly of said tank means for controlling flow of water from saidoutlet end portion to said hot water withdrawal means; and normally openvalve means arranged exteriorly of said tank means for controlling flowof water from said first water intake means to said inlet end portion,whereby when said normally open valve means are closed and said secondnormally closed valve means is opened, said immersion heater may bewithdrawn from said shroud without loss of water from said tank meansand hot water may be withdrawn through said hot water withdrawal meansdirectly from said upper region of said tank means.
 21. A water heatingand storage system according to claim 20, wherein normally open valvemeans are arranged exteriorly of said tank means in said hot waterconduit means upstream and downstream of said pump means, such that whenthe last said valve means are closed said pump means may be removedwithout loss of water from said tank means.
 22. A water heating andstorage system according to claim 12, wherein said hot water conduitmeans includes a conduit extending into said upper region of said tankmeans for delivering hot water thereto, and said second water intakemeans is part comprised by said conduit.
 23. A water heating and storagesystem according to claim 17, wherein said first and second conduits arelocated within said tank means.
 24. A water heating and storage systemaccording to claim 12, wherein said valve means comprises apressure-responsive valve that opens in response to the pressuredifferential created thereacross when the flow rate demand on said hotwater withdrawal means exceeds the maximum flow rate capacity of saidfirst water intake means.
 25. A water heating and storage systemcomprising in combination: a hot water storage tank including arelatively cold water supply inlet for replenishing water withdrawn fromsaid tank; outlet means for withdrawing heated water from said tank atup to a given rate of flow; a conduit system for normally circulatingwater from a lower to an upper region in said tank, said conduit systemhaving heating means for heating water being circulated therethrough,thereby tending to bring the contents of said tank at least at saidupper region up to predetermined withdrawal temperature, said outletmeans being connected inflow communication with said conduit systemdownstream of said heater means; first and second tank water intakemeans in said conduit system upstream of said heater means, said firstintake means being disposed in said lower region for supplying water tosaid heater means at up to an amount below said given rate of flow, andsaid second intake means being disposed in said upper region forsupplying a flow of water from said upper region to said heater meanswhenever the rate at which heated water is withdrawn through said outletmeans exceeds said amount at a rate accommodating for the differencebetween said withdrawal rate and said amount.
 26. A water heating andstorage system according to claim 25, wherein said first intake meansproduces a predetermined pressure differential in said conduit systemupstream of said heater means relative to said tank whenever said firstintake means tends to take iN water exceeding said amount due to the hotwater withdrawal demand on said outlet means exceeding said amount, andsaid second intake means includes valve means operable by said pressuredifferential.
 27. A water heating and storage system according to claim1, wherein the circulation means includes a conduit extending into theupper region of the tank for delivering heated water thereto, and thesecond intake means is in part comprised by said conduit.